Excitation and ionization cross-sections for He I excited states (n = 2 ÷\div 4, Δ\DeltaS = 0)

There are two types of methods for calculation of excitation and ionization of atoms and ions by electrons. A. Sophisticated $\textit{Glose coupling}$ (CC) - $\textit{type}$ methods, such as $\textit{R - matrix}$ [1] and $\textit{CCC}$ (converging elose coupling) [2]. They usually provide sufficiently accurate results. However there are some disagreements and questions in particular cases. B. Rather simple $\textit{Born - type}$ (I order) methods with possible inelusion of exchange and normalization (B). For ions Coulomb field is also ineluded (B). For ions Coulomg field is also included (CB - Coulomb-Born). Generally cross sections obtained by A-methods are preferable, but they are available for very limited number of transitions and atoms. Fast calculations of many transitions required for atomic base in diagnostic code are in fact unreliable. Therefore usage of the B-methods is necessary. Unfortunately the accuracy of calculations by simple B methods is often insufficient. To create the real data bases it is important to und erstand a physical reason of errors and to develope sufficiently simple ways of correction. One very efficient way is the method of K-matrix. It is based on I order B calculation of matrix $\textbf{K}$ for a given set of transitions. Then S-matrix and cross section $\sigma$ are calculated. The B-methods and full K-matrix approach are realized in the coupled programs $\textbf{ATOM-AKM}$ [3,4]. They can be run on PC-486 or higher and require about 10 minutes for 10 channels (transitions) in 10-20 energy points. In this paper we present results of calculations of excitation and ionization cross-sections from He I excited states (nl- n'l' for n, n' = 2 $\div$ 4 without change of spin). Different methods are used and compared. We use atomic units with Ry = 13.60 eV for energy and $\pi$a$^{2}_{0}$ for cross sections